- more freedom in communication
- naked pictures and sexy videos
- the users should be at least 18 years old in order to registers
The adult social networks have one big advantage - the lack of censure. If you don't offend anybody, pretty much you can do and say whatever you want. The forbidden topics don't exist. Try to say "Fuck you" to somebody on Facebook - the message will be deleted together with your account.
This topic is very long to be discussed now. Take a look at this great post or visit one of the adult social networks. Personally, I prefer Zyko.net.